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RE: SCIENCE AND CLASSIFICATION



Dear All,
First of all, I would very strongly recommend that all systematists read the 1998 paper by Eric B. Knox (Biological Journal of the Linnean Society, 63:1-49; entitled "The use of hierarchies as organizational models in systematics"). It's one of those rare "stand-out" papers that occasionally punctuate the systematics literature every decade or so, but not always fully appreciated in the years just after publication.
     Anyway, I have been watching the bird-dinosaur debate for many, many years, and have immersed myself more deeply into it for the past couple of years.  Even among the vast majority, who now agree that birds are dinosaur descendants, there have already been endless debates over whether mononykines are birds, or if Rahonavis is a bird, or Caudipteryx, Protarchaeopteryx, Bambiraptor, Unenlagia ("half-bird"), Microraptor, oviraptors, and so on (and then there's the Protoavis mess which is a story unto itself).
     My contention is that much of this confusion and needless wrangling is no longer due to the lack of information, but rather due to the use of Archaeopteryx as the basalmost bird (the cladistic definition I have accepted, up to now, for the sake of stability in the short-term). But we now have sufficient data to define Aves in a more scientifically rigorous fashion (osteologically), just as was done with Mammalia decades ago. The presence of hair and lactation roughly corresponds to the scientific definition, so there have been no big problems reconciling the two (communication went smoothly, at least until cladistic splintering muddled it up with Mammaliamorpha and the like).
      The new definition of Aves, if done correctly, will do for birds what has so long been successfully done with mammals. The scientific definition will be precise (osteological), but it will roughly coincide with the presence of "vaned" feathers. All those more primitive "protofeathers" on Sinosauropteryx, the newly-discovered pterosaur, and even that bristly-tailed psittacosaur, are apparently just that (PROTOfeather homologs). Whether the structures of Beipiaosaurus are best regarded as advanced protofeathers or primitive vaned feathers remains to be seen. In any case, a precise osteological definition should take precedence over feathers, eggshells, origins of flight, and other characters that fossilize poorly (and that obviously includes bird excrement as well). :-)
     Within this new context, the evolution of brooding and powered flight, the ornithoid eggshell evidence, and so on, will begin to make more sense, and it will also clarify many of the debates that have paleontologists and ornithologists insulting each other in the press and in other public forums (fora?). The whole Longisquama debate is one of the more embarrassing examples.
      I am proposing a long-thought-out, moderate paradigm shift that I believe will enhance stability. Both scientists and the public alike will have to learn that the old "bird = feather possession" idea is inaccurate and out-of-date. But shifting to the possession of "vaned" feathers seems the best way to accomplish a smooth transition (especially with the public). What we now have is confusion and taxonomic instability. The question in my mind is not *whether* we should draw a new line, but *where* it should be drawn. To continue drawing the line at Archaeopteryx (eclectically or cladistically) is a tradition that I think we must abandon for everyone's sake.
      More generally, we are faced with a decision between: (1) an eclectic emphasis on apomorphy (character)-based taxa or (2) a purely cladistic emphasis on node- and stem-based taxa. The latter seems to sacrifice stability of content in favor of stability of definition (definitions which cladists are already fighting over, requiring a new bureaucratic code to settle them, and no sign that its decisions will be widely followed anyway).
       If you look at it from a broad perspective, all classifications are arbitrary and "typological" to some degree, and pure cladism is just promoting a new form of arbitrary "typology". Benton (2000) has already pointed out that in the end, we will be no better off, and thatin many ways we will be much worse off if we follow this path. The pendulum has swung too far already (swinging so far, that even I have been ousted from the "Cladists Club", which is very odd because some eclecticists think I'm too much of a "cladist").
Anyway, I certainly look forward to Mickey Mortimer's upcoming analysis. And I will seriously consider it's outcome as I continue searching for a precise osteological definition of Aves that can be made more precise in the future (as has been done with the Mammalia definition).
         ------ Cheers, Ken Kinman




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